Wireless mobile communications provide the greatest convenience for users to access voice and data services essentially anywhere and anytime. Code Division Multiple Access (“CDMA”) communication systems are one of the most promising digital wireless communication systems that can provide the desired mix of voice and data services. CDMA modulation techniques permit a large number of system users to communicate with one another.
The geographic coverage provided by the communications system is divided into coverage areas referred to as cells, where each cell corresponds to a base station. The cell may be further divided into multiple sectors. Communication channels allocated to a given cell and/or sector are determined according to various known methods. Each base station transmits a pilot signal that serves as a beacon for mobile units that are in the base station's cell.
At the outset of a mobile call, a typical mobile unit sends out a request for services to a base station over an access channel. In response, the typical base station initiates call set-up by using nominally set initial power levels for traffic channels in the forward link (i.e., base station to mobile unit). The nominally set power levels are adjusted using various closed loop and open loop power control methods. Inappropriate initial power levels, however, present risks in setting up the mobile call. For example, inadequate initial power may lead to bursts of errors, resulting in call quality degradation. In some instances, the call may even be dropped in severely interfered environments because of weak initial power levels. A higher initial power level, however, will cause interference with other users and decrease overall system performance and capacity. A drawback of the existing control methods is that they have slow reaction times and can result in dropped calls.